CI: Use latst riot-sys for tests

.github/workflows/test.yml

@@ -91,7 +91,13 @@ jobs:
         board: [native, sltb001a, samr21-xpro, stk3700]
         testdir: ${{ fromJSON(needs.enumerate-wrappers-tests.outputs.list) }}
     steps:
-    # common steps start here
+    - name: Patch local .cargo/config.toml to use current checkout
+      run: |
+        mkdir .cargo
+        echo '[patch.crates-io]' >> .cargo/config.toml
+        echo 'riot-wrappers = { path = ".", version = "*" }' >> .cargo/config.toml
+        echo 'riot-sys = { git = "https://github.com/RIOT-OS/rust-riot-sys" }' >> .cargo/config.toml
+    # common steps start here (kept in sync even though we wouldn't need to patch RIOT's .cargo/config.toml)
     - name: Check out riot-wrappers
       uses: actions/checkout@v3
     - name: Check out RIOT